Image intensifier tubes are well known de,rices that multiply the amount of incident light received and produce an intensified image that can be more easily viewed. Image intensifier tubes are particularly useful in producing visible images from received infrared energy, thereby providing a means for clearly viewing an object at night or during otherwise low light conditions. As a result, devices that utilize image intensifier tubes have been used in a wide variety of industrial and military applications. For example, image intensifier tubes are commonly used for enhancing the night vision of pilots, for photographing astronomical bodies and for providing night vision to the visually handicapped such as persons suffering from retinitis pigmentosa (night blindness).
Image intensifier tubes are well known in the industry by names that are based on the generic generation from which their designs came into being. As a result, image intensifier tubes are typically identified by their generation number, which can be from the Generation 0 tube to the current Generation III (Gen. III) tube. Modern Gen. II image intensifier tubes, the manufacturing of which is the primary application of the present invention, typically include three main components, namely a photocathode, a phosphor screen (anode) and an electron amplifier such as microchannel plate. All three components are disposed within an evacuated housing thereby permitting electrons to flow from the photocathode to the phosphor screen across the electron amplifier. For examples of such devices reference is made to U.S. Pat. No. 5,029,963 entitled "Replacement Device for a Driver's Viewer" issued on Jul. 9, 1991 to C. Naselli et al. and assigned to ITT Corporation the assignee herein. Both Gen. II and Gen. III image intensifiers are discussed in this reference.
In a Gen. II image intensifier tube the phosphor screen and electron amplifier components of the image intensifier tube are contained within a tube subassembly. The tube subassembly and photocathode are traditionally manufactured separately and are then assembled to create the overall image intensifier tube structure. Referring to FIG. 1, a typical Gem II image intensifier tube 10 is shown, such as is currently manufactured by ITT Corporation, the assignee herein. As can be seen, both the tube subassembly 11 and the photocathode 25 are complex structures. The vacuum housing 12 that defines the exterior of the tube subassembly 11 is constructed by the juxtaposition of annular conductive elements and dielectric elements that are brazed together to create an air impervious structure. The lower end of the vacuum housing 12 is sealed by the presence of an screen flange 16 and a centrally positioned fiber optic element 18. The phosphor screen 20, against which electrons will eventually impinge, is disposed across the top surface 22 of the fiber optic element 18 so that the phosphor screen 20 faces the photocathode 25.
The tube subassembly 11 is manufactured in ambient pressure using traditional well-known manufacturing techniques. Similarly the body of the photocathode 25 is separately manufactured in ambient pressure also utilizing traditional well-known manufacturing techniques. When the photocathode 25 is assembled to the tube subassembly 11, the photocathode 25 seals the upper end of the tube subassembly 11, thereby isolating the interior of the image intensifier tube 10 between the photocathode 25 and the phosphor screen 20. Since a vacuum must be present within the image intensifier tube 10, the photocathode 25 must be assembled to the tube subassembly 11 in a clean, evacuated environment, thereby greatly increasing the complexity, time and cost of the overall manufacturing procedure. In the prior art, the assembly of the photocathodes 25 to the tube subassemblies 11 was traditionally done in a single evacuated chamber, two image intensifier tubes at a time. Due to the time involved in loading and unloading the evacuated chamber, evacuating the chamber, baking the chamber and waiting for pans to properly cool, the prior art assembly systems only produced about 2.5 tubes in a twenty-four hour period. Such a labor intensive and slow manufacturing process has added significantly to the cost of image intensifier tubes and has left the image intensifier tubes vulnerable to many potential manufacturing defects that affect the overall reliability of the image intensifier tubes.
An attempt at solving the foregoing problem can be found in U.S. Pat. No. 5,314,363 to Murray entitled AUTOMATED SYSTEM AND METHOD FOR ASSEMBLING IMAGE INTENSIFIER TUBES, issued on May 24, 1994 and assigned to ITT Corporation, the assignee herein. The above invention includes four different processing chambers for accomplishing various portions of the assembly task. Each of the chambers is separated from the other by at least one vacuum gate valve. Such a configuration requires multiple vacuum sources and couplings for selectively evacuating and pressurizing each of the chambers. Multiple vacuum apparatus as well as the gate valve hardware can prove to be prohibitively expensive as they add significantly to the overall manufacturing costs.
It is therefore an objective of the present invention to produce an automated assembly system capable of assembling a high volume of image intensifier tubes in a labor and time efficient manner, while at the same time reducing the amount of hardware necessary in the system.
It is a further object of the present invention to provide an automated assembly system for image intensifier tubes that produces an image intensifier tube of a higher quality and reliability than is available from the prior art.